At present, in a liquid crystal panel which carries out active matrix drive by use of a thin film transistor (hereinafter called TFT), its mainstream is a TN (Twisted Nematic) mode liquid crystal panel in which a p type liquid crystal having positive dielectric anisotropy is aligned horizontally to a substrate when non-voltage is applied, and is driven vertically to the substrate when voltage is applied.
With the progress of late manufacturing technology, the TN mode liquid crystal panel has been improved conspicuously in contrast, a gradation characteristic, and color reproducibility seen from the facade of the liquid crystal panel. However, the TN mode liquid crystal mode has drawbacks that a viewing angle is narrower than CRT, etc., and for this reason there is a problem that the use is restricted.
For the purpose of improving the drawback of the TN mode liquid crystal panel that the viewing angle is narrow, we, the applicant of this invention, developed a MVA (Multidomain Vertical Alignment) type liquid crystal panel which drives horizontally, when voltage is applied, liquid crystal molecules aligned vertically when non-voltage is applied, and in which an alignment direction of the liquid crystal molecules in one pixel is divided into a plurality of parts, and disclosed the structure in Japanese Patent Application Laid-Open No. 10-185836, etc.
The MVA type liquid crystal panel uses an n type liquid crystal having negative dielectric anisotropy and the MVA type liquid crystal panel is provided with domain restriction means for, when voltage is applied, restricting an alignment direction of the liquid crystal so that the direction is set to be a plurality of parts in one pixel.
The domain restriction means incline in advance the liquid crystal molecules at a projection part at a slight angle when non-voltage is applied, by the projection, etc. provided in a part on an electrode. This projection performs a role of a trigger for determining the alignment direction of the liquid crystal molecules when voltage is applied, and any small projection is enough. Incidentally, as the MVA type liquid crystal panel inclines in advance the liquid crystal molecules at a slight angle by the domain restriction means, a rubbing process to a vertical alignment layer or alignment film is unnecessary.
In the MVA type liquid crystal, in a state that non-voltage is applied, most of liquid crystal molecules are aligned vertically to a surface of the substrate, and the transmittance becomes a status of 0 (black state). When an intermediate voltage is applied, the inclination direction of the liquid crystal molecules is determined under the influence of an inclined plane of the projection, and the alignment direction of the liquid crystal in one pixel is partitioned. Accordingly, the intermediate voltage causes an optical characteristic of the liquid crystal in one pixel to average, thereby obtaining a halftone state uniform in all directions. Furthermore, when a predetermined voltage is applied, the liquid crystal molecules are substantially horizontal to change to a white state.
However, in the MVA liquid crystal panel, there is a problem that a response speed when a black state at a drive voltage of about 1V is switched to a low brightness halftone state at a drive voltage of about 2 to 3V is slower than the TN mode liquid crystal panel.
It is considered that this is because, since the rubbing process in the vertical alignment film is not carried out in the MVA type liquid crystal and the alignment directions of the liquid crystals in a fine region direct to various directions in a state that non-voltage is applied, when a drive voltage is low at about 2 to 3V, it takes some time to align the alignment directions of all the liquid crystals to predetermined directions.
Furthermore, when the black state at the drive voltage of about 1V is switched to a high brightness halftone state at the drive voltage of about 3 to 4V, or when the black state at the drive voltage of about 1V is switched to a white state at the drive voltage of about 5V, as the brightness is overshot, there is a problem that a display impression is worse.
It is considered that this is because, as a moment of rotating the alignment direction of the liquid crystal increases at the drive voltage of about 3V or more, the alignment direction of the liquid crystal rotates over the target alignment direction.
Furthermore, when the black state is switched to a halftone state or so, the halftone state or so is affected by not only the black state shortly before that but also a further previous display state, and the brightness may be overshot. It is considered that this is because the alignment state of the liquid crystal in the black state shortly before that differs due to the previous alignment state of the liquid crystal.
Then, it is an object of the present invention to provide a liquid crystal display device having a drive circuit in which when driving the MVA type liquid crystal panel in which n type liquid crystals are aligned vertically, a response time when the black state is switched to the low brightness halftone state is lessened, and the overshoot when the black state is switched to the halftone state or the white state is diminished; and its drive method.